Main Entry: nu·cle·us
Pronunciation: n(y)ü-kl-s
Function: noun
Inflected Form(s): plural nu·clei /-kl-/; also -cle·us·es
Etymology: from modern Latin nucleus "the central part of something," from Latin nucleus "kernel," derived from nux "nut": a central point, group, or mass of something: as a: the small, brighter, and denser part of a galaxy or of the head of a comet b: a cell part that is characteristic of all living things with the exception of viruses, bacteria, and blue-green algae, that is necessary for heredity and for making proteins, that contains the chromosomes, and that is enclosed in a nuclear membrane c: a mass of gray matter or group of neurons in the central nervous system d: the central part of an atom that includes nearly all of the atomic mass and consists of protons and usually neutrons
[nucleus illustration]